Methods and systems for photocuring liquid resin with reduced heat generation

ABSTRACT

In a vat polymerization printer, a beam scanner scans a light beam across a mask and into a tank containing a photo-curable resin. The mask has pixels configurable to be individually transparent or opaque to portions of the light beam, which has a diameter greater than a cross-sectional dimension of the pixels of the mask. During an exposure time duration, a first subset of the pixels are controlled to be transparent at locations corresponding to the cross section of a three-dimensional object to be printed, while a second subset of the pixels are controlled to be opaque at locations not corresponding to the cross section of the three-dimensional object. The beam scanner is controlled to scan the light beam across the mask such that the light beam is always incident on at least one of the pixels of the mask that are controlled to be transparent.

RELATED APPLICATIONS

This is a NONPROVISIONAL of, claims priority to, and incorporates byreference U.S. Provisional Application No. 63/200,258, filed 24 Feb.2021.

FIELD OF THE INVENTION

The present invention relates to the printing of three-dimensionalobjects by photo-curing a liquid resin, and more particularly relates toreducing heat imparted into the liquid resin by a light source.

BACKGROUND

One obstacle encountered in the three-dimensional printing of objectsthat involves the curing of photo-curable liquid resin is the heating ofthe liquid resin. Not only is the curing of photo-curable liquid resinan exothermic reaction (which locally heats regions of the photo-curableliquid resin where the curing takes place), but the irradiation of amask by a light source, typically an ultra-violet (UV) light source,also causes heating of the mask. As the mask is located in closeproximity to the liquid resin, any heating of the mask also leads to thefurther heating of the photo-curable liquid resin.

If the liquid resin temperature exceeds a critical temperature, portionsof the resin may start to cure even in the absence of UV light, leadingto defects in the printed objects. In prior approaches to prevent theliquid resin temperature from exceeding this critical temperature, theprinting process may be periodically halted to allow the photo-curableliquid resin to cool, with the consequence of reducing the throughput ofthe printing process. Also in prior approaches, a resin circulatorysystem may be employed to cool the heated resin. While heat removal viaa resin circulatory system may effectively achieve the desired effect ofcontrolling the liquid resin temperature, approaches described hereincontrol the temperature of the liquid resin through other or additionalmeans.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a vat polymerization printerincludes a tank configured for containing a photo-curable liquid resin,a light source configured to emit a light beam, and a mask positionedbetween the light source and the tank and having pixels configurable tobe individually transparent or opaque to portions of the light beam.Preferably, a diameter of a cross section of the light beam is greaterthan a cross-sectional dimension of each of the respective pixels. Abeam scanner is configured to scan the light beam across the mask, and aprocessor operating under stored processor-executable instructionscontrols the vat polymerization printer to print a cross section of athree-dimensional object by: controlling, during an exposure timeduration, a first subset of the pixels to be transparent at locationscorresponding to the cross section of the three-dimensional object, anda second subset of the pixels to be opaque at locations notcorresponding to the cross section of the three-dimensional object; andcontrolling, during the exposure time duration, the beam scanner to scanthe light beam across the mask such that the light beam is alwaysincident on at least one of the pixels of the mask that are controlledto be transparent.

In various embodiments, the diameter of the cross section of the lightbeam may be at least ten times or at least a hundred times thecross-sectional dimension of each of the respective pixels of the mask.Further, the light source may include a laser source configured to emita laser beam; and a beam expander configured to generate the light beamfrom the laser beam, wherein the diameter of the cross section of thelight beam is greater than a diameter of a cross section of the laserbeam.

In various embodiments, the processor-executable instructions mayfurther cause the processor to determine a scan path for the light beambased on respective locations of the pixels that are controlled to betransparent during the exposure time duration. Also, during the exposuretime duration, the processor-executable instructions may further causethe processor to turn off the light source while the beam scannerrepositions the light beam between a first region of the mask thatincludes at least some pixels that are controlled to be transparent to athird region of the mask that includes at least some pixels that arecontrolled to be transparent, the third region of the mask beingseparate from the first region of the mask by a second region of themask that includes only pixels that are controlled to be opaque. And, instill further embodiments, the processor-executable instructions mayfurther cause the processor to control a blocking element to block thelight beam while the beam scanner repositions the light beam from afirst region of the mask that includes at least some pixels that arecontrolled to be transparent to the third region of the mask. In thevarious embodiments, the pixels may be electrically modulated liquidcrystal pixel elements.

In various embodiments, the vat polymerization printer may furtherinclude a transparent backing member disposed between the mask and aflexible membrane. Additionally, an extraction plate may be disposedwithin the tank, and during printing the three-dimensional object formedfrom cured portions of the photo-curing liquid resin is affixed to theextraction plate. A height adjustor may be configured to control avertical position of the extraction plate above the mask.

Other embodiments of the invention provide a vat polymerization printerthat includes a tank configured for containing a photo-curable liquidresin, a light source configured to emit a light beam, and a mask havingpixels configurable to be individually transparent or opaque to portionsof the light beam. A diameter of a cross section of the light beam isgreater than a cross-sectional dimension of each of the respectivepixels and a beam scanner is configured to scan the light beam acrossthe mask. A processor of a controller executes instructions to controlthe vat polymerization printer to print a cross section of athree-dimensional object by controlling, during an exposure timeduration, a first subset of the pixels to be transparent at locationscorresponding to the cross section of the three-dimensional object, anda second subset of the pixels to be opaque at locations notcorresponding to the cross section of the three-dimensional object; andcontrolling, during the exposure time duration, the beam scanner to scanthe light beam across at least one region of the mask having pixels thatare controlled to be transparent, wherein at most ten percent of thepixels that are controlled to be opaque are scanned by the light beamduring the printing of the cross section of the three-dimensionalobject.

In various embodiments, the processor of the controller may furtherexecute instructions to control the beam scanner to repeatedly scan thelight beam across a first region of the mask that includes at least somepixels that are controlled to be transparent, followed by controllingthe beam scanner to scan the light beam along a beam path within asecond region that separates the first region from a third region, thesecond region including only pixels that are controlled to be opaque,and the third region including at least some pixels that are controlledto be transparent, and the beam path within the second region being ashortest path that connects a beam path in the first region and a beampath in the third region, and followed by controlling the beam scannerto repeatedly scan the light beam across the third region of the mask.Repeatedly scanning the light beam across the first region of the maskcomprises at least one of a raster scan or a back and forth scan of thefirst region of the mask, and repeatedly scanning the light beam acrossthe third region of the mask comprises at least one of a raster scan ora back and forth scan of the third region of the mask.

Another embodiment of the invention provides for printing a crosssection of a three-dimensional object in a photocuring region of a vatpolymerization printer that includes (i) a tank configured forcontaining a photo-curable liquid resin, (ii) a flexible membranedefining a bottom boundary of the photocuring region, (iii) a lightsource configured to emit a light beam, (iv) a beam scanner configuredto scan the light beam, and (v) a mask disposed between the beam scannerand the flexible membrane and having pixels configurable to beindividually transparent or opaque to portions of the light beam,wherein a diameter of a cross section of the light beam is greater thana cross-sectional dimension of each of the respective pixels. Accordingto the printing process, during an exposure time duration a first subsetof the pixels are controlled to be transparent at locationscorresponding to the cross section of the three-dimensional object, asecond subset of the pixels are controlled to be opaque at locations notcorresponding to the cross section of the three-dimensional object, andthe light beam is scanned across at least one region of the mask havingat least some pixels that are controlled to be transparent and into thephotocuring region, wherein at most ten percent of the pixels that arecontrolled to be opaque are scanned by the light beam during theprinting of the cross section of the three-dimensional object.

In this printing process, during the exposure time duration, and as aresult of the control of the first and second subset of the pixels, afirst region of the mask includes at least some pixels that arecontrolled to be transparent, a second region of the mask includes onlypixels that are controlled to be opaque, and a third region of the maskincludes at least some pixels that are controlled to be transparent, andthe scanning of the light beam comprises repeatedly scanning the lightbeam across the first region of the mask and into the photocuring regionthrough pixels in the first region that are controlled to betransparent, followed by scanning the light beam along a shortest path,within the second region, that connects a beam path in the first regionand a beam path in the third region, and followed by repeatedly scanningthe light beam across the third region of the mask and into thephotocuring region through pixels in the third region that arecontrolled to be transparent. Repeatedly scanning the light beam acrossthe first region of the mask comprises at least one of a raster scan ora back and forth scan of the first region of the mask, and whereinrepeatedly scanning the light beam across the third region of the maskcomprises at least one of a raster scan or a back and forth scan of thethird region of the mask.

Alternatively, or in addition, during the exposure time duration, and asa result of the control of first and second subset of the pixels, afirst region of the mask includes at least some pixels that arecontrolled to be transparent, a second region of the mask includes onlypixels that are controlled to be opaque, and a third region of the maskincludes at least some pixels that are controlled to be transparent, andthe scanning of the light beam comprises repeatedly scanning the lightbeam across the first region of the mask and into the photocuring regionthrough pixels of the first region that are controlled to betransparent, repositioning the light beam from the first region of themask to the third region of the mask without scanning the second regionof the mask, and repeatedly scanning the light beam across the thirdregion of the mask and into the photocuring region through pixels of thethird region that are controlled to be transparent. Repeatedly scanningthe light beam across the first region of the mask comprises at leastone of a raster scan or a back and forth scan of the first region of themask, and wherein repeatedly scanning the light beam across the thirdregion of the mask comprises at least one of a raster scan or a back andforth scan of the third region of the mask.

During the exposure time duration of the printing process, a totalnumber of pixels in the first subset of the pixels may be less than atotal number of pixels in the second subset of the pixels.

Still another embodiment of the invention provides for printing a crosssection of a three-dimensional object in a photocuring region of a vatpolymerization printer that includes (i) a tank configured forcontaining a photo-curable liquid resin, (ii) a flexible membranedefining a bottom boundary of the photocuring region, (iii) a lightsource configured to emit a light beam, (iv) a beam scanner configuredto scan the light beam, and (v) a mask disposed between the beam scannerand the flexible membrane and having pixels configurable to beindividually transparent or opaque to portions of the light beam,wherein a diameter of a cross section of the light beam is greater thana cross-sectional dimension of each of the respective pixels. Theprocess includes controlling, during an exposure time duration, a firstsubset of the pixels to be transparent at locations corresponding to thecross section of the three-dimensional object, and a second subset ofthe pixels to be opaque at locations not corresponding to the crosssection of the three-dimensional object; and scanning, during theexposure time duration, the light beam across at least one region of themask having at least some pixels that are controlled to be transparentand into the photocuring region, wherein the scanning compensates for anon-uniformity in a light transmission across respective pixels in theat least one region of the mask by at least one of: (i) varying a lightintensity of the light beam while the light beam is scanned over the atleast one region, (ii) varying a scan speed of the light beam while thelight beam is scanned over the at least one region, or (iii) varying anumber of times the light beam is repeatedly scanned over the at leastone region.

These and further embodiments of the present invention are describedmore fully below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example and without limitingthe scope of the invention, with reference to the accompanying drawingswhich illustrate embodiments of it, in which:

FIG. 1 depicts a cross-section of a three-dimensional (3D) printingsystem, in accordance with one embodiment of the invention.

FIG. 2 depicts components of a light source, in accordance with oneembodiment of the invention.

FIG. 3A depicts transparent and opaque regions of a mask, in accordancewith one embodiment of the invention.

FIG. 3B depicts a magnified view of a portion of the mask depicted inFIG. 3A, in which individual transparent and opaque pixels are visible,in accordance with one embodiment of the invention.

FIG. 4A depicts a beam spot of a light beam illuminating a portion ofthe mask depicted in FIG. 3A, in accordance with one embodiment of theinvention.

FIG. 4B depicts a magnified view of a portion of the mask and beam spotdepicted in FIG. 3A, in which individual transparent and opaque pixelsare visible, in accordance with one embodiment of the invention.

FIG. 5 depicts the beam path of a light beam performing a raster scan ofa restricted region of the mask (depicted in FIG. 3A) with transparentpixels, in accordance with one embodiment of the invention.

FIG. 6 depicts transparent and opaque regions of a mask, in accordancewith one embodiment of the invention.

FIG. 7 depicts a back and forth scan of a restricted region of the mask(depicted in FIG. 6) with transparent pixels, in accordance with oneembodiment of the invention.

FIG. 8 depicts transparent and opaque regions of a mask, in accordancewith one embodiment of the invention.

FIG. 9 depicts the beam path of a light beam scanning the mask of FIG.8, in which the light beam repeatedly scans a first region and a secondregion with transparent pixels, in accordance with one embodiment of theinvention.

FIG. 10 depicts the beam path of a light beam scanning the mask of FIG.8, in which the light beam repeatedly scans a first region and a secondregion with transparent pixels, and further scans a shortest path thatconnects a beam path in the first region with a beam path in the secondregion, in accordance with one embodiment of the invention.

FIG. 11 depicts a 3D printing system with two light beams, eachconfigured to scan a mask of the vat polymerization printer, inaccordance with one embodiment of the invention.

FIG. 12A depicts a flow chart of a method to print a cross section of athree-dimensional object with reduced heat generation, in accordancewith one embodiment of the invention.

FIG. 12B depicts a flow chart of another method to print a cross sectionof a three-dimensional object with reduced heat generation, inaccordance with one embodiment of the invention.

FIG. 13A depicts a flow chart of a method to scan a light beam across asurface of a mask of a 3D printing system, in accordance with oneembodiment of the invention.

FIG. 13B depicts a flow chart of another method to scan a light beamacross a surface of a mask of a 3D printing system, in accordance withone embodiment of the invention.

FIG. 14 depicts a flow chart of a method to print a cross section of athree-dimensional object with reduced heat generation, and to furthercompensate, during the printing, for the non-uniformity in the lighttransmissivity across respective pixels of a mask of a 3D printingsystem, in accordance with one embodiment of the invention.

FIG. 15 depicts components of a computer system in which computerreadable instructions instantiating the methods of the present inventionmay be stored and executed.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings that form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. It is understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention. Descriptionsassociated with any one of the figures may be applied to differentfigures containing like or similar components/steps. While the sequencediagrams each present a series of steps in a certain order, the order ofsome of the steps may be changed.

In one embodiment of the invention, the need to cool the liquid resin isreduced by reducing the degree to which the liquid resin is heated.While the heating of the liquid resin due to the exothermic reactionthat takes place during the curing of resin cannot be avoided, theheating of the mask can be reduced by selectively illuminating onlyregions of the mask with transparent pixels and/or minimizing theillumination of the regions of the mask with opaque pixels. These andother embodiments of the invention are more fully described inassociation with the drawings below.

FIG. 1 depicts a cross-section of a three-dimensional (3D) printingsystem 100 (also called a vat polymerization printer), in whichelectromagnetic radiation (e.g., ultra-violet light) is used to curephoto-curable liquid resin 18 in order to fabricate object 22 (e.g., a3D object). Object 22 may be fabricated layer by layer; that is, a newlayer of object 22 may be formed by photo-curing a layer 34 of liquidresin 18 adjacent to the bottom surface of object 22, the object may beraised by extractor plate 20, allowing a new layer of photo-curingliquid resin 18 to be drawn under the newly formed layer; and theprocess repeated to form additional layers.

The 3D printing system 100 includes tank 10 for containing thephoto-curable liquid resin 18. The bottom of tank 10 includes a bottomopening 12 to allow electromagnetic radiation (e.g., filtered light beam32) from light source 24 to enter into tank 10. An optionalradiation-transparent backing member 16 (e.g., borosilicate glass or atoughened glass such as an alkali-aluminosilicate glass of approximately100 μm thickness) may be used to seal the tank opening 12 (i.e., toprevent the photo-curing liquid polymer 18 from leaking out of tank 10),while at the same time, allowing electromagnetic radiation to enter intotank 10 in order to cure the liquid polymer.

One challenge faced by 3D printing systems of the present kind is thatin addition to adhering to the object 22, newly formed layers tend toadhere to the bottom of tank. Consequently, when the extraction plate 20to which the object is attached is raised by height adjustor 39, thenewly formed layer could tear and/or become dissociated from the object22. To address this issue, a flexible membrane 14 may be disposedadjacent to backing member 16 (if present) or may form the bottom of thetank (if no backing member is used). Flexible membrane 14 may be formedof silicone or another material, and optionally, coated with a non-stickmaterial such as polytetrafluoroethylene (PTFE) to reduce the likelihoodfor the newly formed layer to adhere to the bottom of tank 10. Theflexible membrane 14 is transparent (or nearly so) to the wavelength ofradiation emitted by the light source 24 so as to allow that radiationto enter into tank 10 in order to cure the liquid polymer 18.

A mask 30 may be disposed to spatially filter the radiation that isincident on layer 34, so that specific regions of the liquid resin 18,that correspond to the cross section of the object 22 being printed, arecured. Mask 30 may be a transmissive spatial light modulator, such as aliquid crystal display (LCD) with a two-dimensional array of addressablepixels. As will be more clearly described below, certain ones of thepixels of the mask may be controlled to be transparent, while others maybe controlled to be opaque. Transparent pixels allow radiation to passthrough the mask 30 at certain spatial locations of mask 30 and intotank 10, consequently curing corresponding portions (voxels) of theliquid resin 18, while opaque pixels prevent radiation from passingthrough certain spatial locations of mask 30, thereby avoiding curing ofcorresponding portions (voxels) of the liquid resin 18.

A beam scanner 26 may scan light beam 28 across mask 30. As will bedescribed in more detail below, beam scanner 26 may be controlled bycontroller 36 to selectively scan light beam 28 across regions of mask30 with transparent pixels, while substantially avoiding regions of mask30 with only opaque pixels. Beam scanner 26 may be an x-y scanner, suchas a galvo scanner (also known as a galvanometer scanner). In apreferred embodiment (although not depicted in FIG. 1), the distanceseparating beam scanner 26 from mask 30 is substantially greater thanthe lateral dimensions of mask 30 so that light beam 28 is incident uponmask 30 at substantially 90° regardless of whether light beam 28 isscanning peripheral regions of mask 30 or central regions of mask 30.Such placement of the beam scanner 26 relative to the mask 30, alongwith a minimal separation between mask 30 and resin layer 34 decreasethe effects of diffraction as light passes through mask 30, therebyincreasing the accuracy to which object 22 can be printed.

Controller 36 may be communicatively coupled to mask 30, beam scanner26, light source 24 and height adjustor 39 via control signal paths 38a, 38 b, 38 c and 38 d, respectively (e.g., electrical signal paths).Controller 36 may control the addressable pixels of mask 30 such thatthe transparent pixels of mask 30 correspond to a cross section of anobject to be printed (e.g., a layer of that object). Controller 36 maycontrol beam scanner 26 to selectively scan a light beam across regionsof mask 30 with transparent pixels, while substantially avoiding regionsof mask 30 with only opaque pixels. Often times, the transparent pixelsonly account for a portion of the total pixels (e.g., 30%, 50%, etc.).Assuming those transparent pixels are aggregated in certain regions(which is often the case), only those regions of the mask are scanned,which substantially reduces the number of opaque pixels that areirradiated unnecessarily, in turn reducing the heating of mask 30 andresin 18. Specific examples of the scanning of light beam 28 will beprovided below.

Controller 36 may also control light source 24. For instance, to furtherreduce the heating of mask 30, controller 36 may turn off light source24 while light beam 28 is being repositioned by scanner 26 from oneregion of mask 30 with transparent pixels to another region of mask 30with transparent pixels. Controller 36 may also control height adjustor39 to control the vertical position of height extractor 20, andconsequently of object 22 that is affixed to height extractor 20.

As depicted in FIG. 2, light source 24 may include laser source 40 thatgenerates laser beam 42, and a beam expander 44 which transforms thecollimated and focused laser beam 24 into a collimated and defocusedlight beam 28. For the sake of conciseness, collimated and defocusedlight beam 28 is simply referred to as “light beam” 28 throughout thedescription. As depicted in FIG. 2, a diameter, d2, of the cross sectionof light beam 28 may be larger than a diameter, d1, of the cross sectionof laser beam 42.

FIG. 3A depicts mask 30 during an exposure time duration, during whichtime, some pixels of mask 30 are controlled to be in a transparent statewhile other pixels of mask 30 are controlled to be in an opaque state(although mask 30 is not depicted at a level of detail in which theindividual pixels are visible). For clarity of illustration, region 50of mask 30 with opaque pixels is depicted with a gray shading, whileregion 52 of mask 30 with transparent pixels is depicted in white (i.e.,without any shading). It is understood that a light beam scanning acrossmask 30 will pass through region 52 of the mask (and cure portions oflayer 34 of liquid resin 18), while the light beam will not pass throughregion 50 of the mask. The shape of region 52 is chosen to approximatelycorrespond to a cross section 53 of an object that is to be printed (seecross section 53 depicted as an inset in FIG. 3A). Typical dimensions ofmask 30 (i.e., in the diagonal direction) may measure 13.3 inches, whileit is contemplated that the dimensions of mask 30 will increase in thefuture, allowing for the printing of objects with larger dimensions.

FIG. 3B depicts a magnified view of portion 54 of the mask 30 depictedin FIG. 3A, in which individual pixels (e.g., electrically modulatedliquid crystal pixel elements) are visible in the magnified view.Reference numeral 56 labels one of the opaque pixels, while referencenumeral 58 labels one of the transparent pixels of mask 30. For clarityof illustration, opaque pixels are depicted in gray shading, while clearpixels are depicted in white (i.e., without any shading). It isunderstood that the visualization of pixels in FIG. 3B is merely aschematic illustration, and may not depict an actual representationthereof. For instance, pixels are depicted with square boundaries inFIG. 3B, but other boundary shapes are possible, such as a rectangularboundary, an oval boundary, a circular boundary, etc. The physicalconstruction of a pixel (e.g., liquid crystal sandwiched between twoelectrodes) is well known in the art, and will not be discuss herein forthe sake of conciseness.

FIG. 4A depicts cross section 60 of light beam 28 at the surface of mask30. For conciseness of discussion, cross section 60 may be referred toas a “beam spot,” but if the “illuminated” area of mask 30 comprisestransparent pixels, it is understood that the “beam spot” may notactually be visible, as light beam 28 may shine through mask 30 withoutreflecting off of the surface of mask 30.

FIG. 4B depicts a magnified version of portion 54 of the mask 30depicted in FIG. 3B. As shown in FIG. 4B, the diameter, d2, of beam spot60 may be an order of magnitude (or more) greater than the crosssectional dimension, w, of each of the respective pixels. In oneembodiment of the invention, the diameter, d2, is at least ten times thecross-sectional dimension, w, of each of the respective pixels. Inanother embodiment of the invention, the diameter, d2, is at least onehundred times the cross-sectional dimension, w, of each of therespective pixels. As an example, w may measure 25-150 μm, whereas d2may measure 10 mm. In another embodiment of the invention, the diameter,d2, of beam spot 60 may be dynamically adjusted based on thecross-sectional dimensions of the object to be fabricated. If thecross-sectional dimensions of the object to be fabricated are on theorder of centimeters, d2 may measure 1 centimeter. If thecross-sectional dimensions of the object to be fabricated are on theorder of millimeters, d2 may measure 1 millimeter. Such dynamicaladjustment of the beam spot diameter may further reduce the illuminationof opaque pixels (and consequently reduce the heating of the liquidresin), while preserving the throughput for objects having largercross-sectional dimensions.

FIG. 5 depicts beam path 62 of a light beam performing a raster scan ofa transparent region 52 of mask 30. Beam spot 60 continuously travels(i.e., sweeps) across the surface of mask 30 along beam path 62. Thebeam path 62 may be determined by controller 36 based on the locationsof the transparent pixels in mask 30 (i.e., beam path 62 is chosen toilluminate the transparent pixels of mask 30 in a uniform manner). It isunderstood that a thin border of opaque pixels surrounding transparentregion 52 may also be illuminated, in order to allow for the possibilityfor some inaccuracy in the control of the location of beam spot 60 onmask 30, and also allowing for the possibility for some inaccuracy inthe control of the beam spot diameter. However, the number of opaquepixels (e.g., in the thin border) that are illuminated may be minimizedto minimize the heating of mask 30 by light beam 28. In a scenario wheretransparent pixels are concentrated in a single region (such as in theexample of FIG. 5), it is possible that no more than 1% of the opaquepixels are illuminated by light beam 28 (during the printing of a singlecross section of object 22). In a scenario where transparent pixels areconcentrated in multiple regions (such as in the example of FIG. 8), itis possible that no more than 10% of the opaque pixels are illuminated(during the printing of a single cross section of object 22). It isunderstood that the beam spot of successive “rows” of the raster scanmay overlap by a few pixels so as to allow for region 52 to be scannedwith uniform light intensity (i.e., uniform intensity, as averaged outover time). Further, it is understood that the beam path 62 depicted inFIG. 5 may be traced out several times by light beam 28 (one time in thedirection depicted in FIG. 5; the next time, following the path in thereverse direction; and then in the next time, following the directiondepicted in FIG. 5, and so on). Repeatedly performing a fast scan of aregion (e.g., performing 10 quick traversals through beam path 62) maybe more optimal than performing a single slow scan of a region (e.g.,perform a single traversal through beam path 62), as the heating ofresin 18 may be spread out more uniformly across layer 34.

FIG. 6 depicts opaque regions 50 and transparent regions 52 of mask 30,during another exposure time duration. In FIG. 6, the transparentregions 52 are arranged within a “thin strip” with width dimensions lessthan the diameter, d2, of the beam spot 60. Consequently, as shown inFIG. 7, light beam 28 may be repeatedly scanned in a “back and forth”manner along beam path 62 so as to illuminate transparent regions 52 ofmask 30. During such scanning, it is understood that some opaque pixelsin opaque region 50 may also be scanned by light beam 28 (i.e., whenlight beam 28 passes from one transparent region to another), but numberof opaque pixels that are scanned is minimized to a large degree, ascompared to the scenario in which the entire mask were raster scanned.

FIG. 8 depicts opaque regions 50 and transparent regions 52 of mask 30,during another exposure time duration. In the example of FIG. 8, region64 a of mask 30 includes a high concentration of transparent pixels,likewise for region 64 c, and region 64 a is separated from region 64 cby region 64 b with only opaque pixels. FIG. 9 depicts the beam paths 62a, 62 b that may be followed by light beam 28 to scan the transparentpixels of mask 30. In one scenario, light beam 28 may scan thetransparent pixels within region 64 a by repeatedly following beam path62 a. Beam scanner 26 may then reposition light beam 28 to region 64 cwithout light beam 28 scanning region 64 b with only opaque pixels.During the repositioning of light beam 28, controller 36 may turn offlight source 24 or control a blocking element (not depicted) to blocklight beam 28. For instance, the blocking element may include a shutterof light source 24 that can be controlled by controller 36 to blocklight beam 28. After the repositioning, light beam 28 may scan thetransparent pixels within region 64 c by repeatedly following beam path62 b. It is noted that the scanning speed of laser beam 28 within region64 a may differ from the scanning speed of laser beam 28 within region64 c. For instance, smaller regions may be scanned at a slower speedthan larger regions.

FIG. 10 depicts a scanning scheme that minimizes the scanning of opaquepixels without the need to turn off light source 24 or block light beam28. In the scanning scheme of FIG. 10, light beam 28 similarly scans thetransparent pixels within region 64 a by repeatedly following beam path62 a. However, during the repositioning of the light beam 28 from region64 a to 64 c, light beam 28 scans along beam path 62 b. Beam path 62 bmay be a shortest path through region 64 b that connects beam path 62 awithin region 64 a and beam path 62 b within region 64 c. After therepositioning, light beam 28 may scan the transparent pixels withinregion 64 c by repeatedly following beam path 62 b.

FIG. 11 depicts a 3D printing system 101 that employs multiple lightbeams (e.g., two light beams) for scanning mask 30. Beam scanner 26 amay scan light beam 28 a from light source 24 a selectively acrosscertain regions of mask 30, and depending on whether the scanned pixelsare transparent or opaque, filtered light beam 32 a may be transmittedthrough mask 30 and cure a portion of resin in layer 34. Similarly, beamscanner 26 b may scan light beam 28 b from light source 24 b selectivelyacross other regions of mask 30, and depending on whether the scannedpixels are transparent or opaque, filtered light beam 32 b may betransmitted through mask 30 and cure a portion of resin in layer 34. Asan example, light beam 28 a could follow beam path 62 a in FIG. 10, andlight beam 28 b could follow beam path 62 b in FIG. 10. While increasingthe cost of 3D printing system 101, multiple light beams may provide fora faster throughput (i.e., printing speed) as compared a 3D printingsystem that employs a single light beam. For ease of depiction,controller 36 has not been illustrated in FIG. 11, but it should beapparent that controller 36 may be used to control beam scanner 26 a and26 b and other previously described components of FIG. 11.

FIG. 12A depicts flow chart 102 of a method to print a cross section ofa three-dimensional object with reduced heat generation. At step 104,controller 36 may control, during an exposure time duration, a firstsubset of the pixels to be transparent at locations corresponding to thecross section of a (to be printed) three-dimensional object, and asecond subset of the pixels to be opaque at locations not correspondingto the cross section of the three-dimensional object. At step 106,controller 36 may control beam scanner 26, during the same exposure timeduration as step 104, to scan light beam 28 across at least one regionof the mask having at least some pixels that are controlled to betransparent. The scanning may be performed such that light beam 28 isalways incident on at least one of the pixels of mask 30 that iscontrolled to be transparent during the printing of the cross section ofthe three-dimensional object. Such a scanning scheme was illustrated inFIGS. 5, 7 and 9. The heat reduction, of course, is most pronounced whenthe transparent pixels only account for a small (or smaller) portion ofthe total number of pixels (e.g., less than 30%-50% of the total numberof pixels).

FIG. 12B depicts flow chart 108 of another method to print a crosssection of a three-dimensional object with reduced heat generation. Atstep 110, controller 36 may control, during an exposure time duration, afirst subset of the pixels to be transparent at locations correspondingto the cross section of a (to be printed) three-dimensional object, anda second subset of the pixels to be opaque at locations notcorresponding to the cross section of the three-dimensional object. Atstep 112, controller 36 may control beam scanner 26, during the sameexposure time duration as step 110, to scan light beam 28 across atleast one region of the mask having at least some pixels that arecontrolled to be transparent. The scanning may be performed such that atmost ten percent of the pixels that are controlled to be opaque arescanned by light beam 28 during the printing of the cross section of thethree-dimensional object. Such a scanning scheme was illustrated inFIGS. 5, 7, 9 and 10. Again, the heat reduction is most pronounced whenthe transparent pixels only account for a small (or smaller) portion ofthe total number of pixels (e.g., less than 30%-50% of the total numberof pixels).

FIG. 13A depicts flow chart 200 of a method to scan light beam 28 acrossa surface of a mask of a 3D printing system. At step 202, light beam 28may be repeatedly scanned across a first region of mask 30 that includesat least some transparent pixels. Step 202 was described above by thescanning of transparent pixels within region 64 a in FIG. 9. At step204, light beam 28 may be repositioned from the first region to a thirdregion of the mask that includes at least some transparent pixels,without scanning a second region of the mask that separates the firstregion from the third region, the second region of the mask includingonly opaque pixels. Step 204 was described above in FIG. 9 in therepositioning of light beam 28 from region 64 a to region 64 c. At step206, light beam 28 may be repeatedly scanned across the third region ofthe mask that includes at least some transparent pixels. Step 206 wasdescribed above by the scanning of transparent pixels within region 64 cin FIG. 9.

FIG. 13B depicts flow chart 208 of a method to scan light beam 28 acrossa surface of a mask of a 3D printing system. At step 210, light beam 28may be repeatedly scanned across a first region of mask 30 that includesat least some transparent pixels. Step 210 was described above by thescanning of transparent pixels within region 64 a in FIG. 10. At step212, light beam 28 may be scanned along a path within a second regionthat separates the first region from a third region, the second regionincluding only opaque pixels, and the third region including at leastsome transparent pixels, the path being a shortest path that connects abeam path in the first region and a beam path in the third region. Step212 was described above in FIG. 10 by the scanning of light beam 28along beam path 62 c. At step 214, light beam 28 may be repeatedlyscanned across the third region of the mask that includes at least sometransparent pixels. Step 214 was described above by the scanning oftransparent pixels within region 64 c in FIG. 10.

In practice, there may be some non-uniformity in the lighttransmissivity across respective pixels of the mask (e.g., more than 10%variation across the pixels). For example, even if a pixel is controlledto be (fully) transparent, it may only be 95% transparent to light dueto defects, aging of the pixel, etc. Therefore, for the sake of clarity,it is noted that the above-mentioned “transparent pixel” may refer to apixel that is 100% transparent to light, 99% transparent to light, 95%transparent to light, etc. Likewise, the above-mentioned “opaque pixel”may refer to a pixel that is 100% opaque to light, 99% opaque to light,95% opaque to light, etc.

FIG. 14 depicts flow chart 250 of a method for printing a cross sectionof a three dimensional object that includes scanning light beam 28across a surface of a mask of a 3D printing system in such a way thatthe scanning compensates for the non-uniformity in the lighttransmissivity across respective pixels of the mask. At step 252, auniformity in a light transmissivity across respective pixels of themask may be assessed. Such an assessment may comprise controlling allpixels to be (fully) transparent, illuminating the entire mask (e.g.,scanning a light beam across the entire mask), and measuring theintensity of the light transmitted by each of the pixels. During thisinitial assessment, it is assumed that the light intensity of the lightbeam itself is fairly uniform, regardless of whether the light beam isshining near the central region or the peripheral regions of the mask.The respective locations of any pixels with a less-than-expected lightintensity may be identified (e.g., an attenuated light intensityrelative to other pixel elements).

At step 254, controller 36 may control, during an exposure timeduration, a first subset of the pixels to be transparent at locationscorresponding to the cross section of a (to be printed)three-dimensional object, and a second subset of the pixels to be opaqueat locations not corresponding to the cross section of thethree-dimensional object. At step 256, controller 36 may control beamscanner 26, during the same exposure time duration as step 104, to scanlight beam 28 across at least one region of the mask having at leastsome pixels that are controlled to be transparent. The scanning may beperformed in a manner that compensates for the non-uniformity in thelight transmission across respective pixels in the at least one regionof the mask. The compensation may include: (i) varying a light intensityof the light beam while the light beam is scanned over the at least oneregion, (ii) varying a scan speed of the light beam while the light beamis scanned over the at least one region, or (iii) varying a number oftimes the light beam is repeatedly scanned over the at least one region.More specifically, for those regions where the pixels are known (via theassessment in step 252) to output an attenuated light output, the lightintensity of the light beam may be increased, the scanning speed of thelight beam may be decreased and/or the number of scanning passes throughthose regions may be increased so as to compensate for the attenuatedlight output.

As is apparent from the foregoing discussion, aspects of the presentinvention involve the use of various computer systems and computerreadable storage media having computer-readable instructions storedthereon. FIG. 15 provides an example of system 300 that may berepresentative of any of the computing systems (e.g., controller 36)discussed herein. Note, not all of the various computer systems have allof the features of system 300. For example, certain ones of the computersystems discussed above may not include a display inasmuch as thedisplay function may be provided by a client computer communicativelycoupled to the computer system or a display function may be unnecessary.Such details are not critical to the present invention.

System 300 includes a bus 302 or other communication mechanism forcommunicating information, and a processor 304 coupled with the bus 302for processing information. Computer system 300 also includes a mainmemory 306, such as a random access memory (RAM) or other dynamicstorage device, coupled to the bus 302 for storing information andinstructions to be executed by processor 304. Main memory 306 also maybe used for storing temporary variables or other intermediateinformation during execution of instructions to be executed by processor304. Computer system 300 further includes a read only memory (ROM) 308or other static storage device coupled to the bus 302 for storing staticinformation and instructions for the processor 304. A storage device310, for example a hard disk, flash memory-based storage medium, orother storage medium from which processor 304 can read, is provided andcoupled to the bus 302 for storing information and instructions (e.g.,operating systems, applications programs and the like).

Computer system 300 may be coupled via the bus 302 to a display 312,such as a flat panel display, for displaying information to a computeruser. An input device 314, such as a keyboard including alphanumeric andother keys, may be coupled to the bus 302 for communicating informationand command selections to the processor 304. Another type of user inputdevice is cursor control device 316, such as a mouse, a trackpad, orsimilar input device for communicating direction information and commandselections to processor 304 and for controlling cursor movement on thedisplay 312. Other user interface devices, such as microphones,speakers, etc. are not shown in detail but may be involved with thereceipt of user input and/or presentation of output.

The processes referred to herein may be implemented by processor 304executing appropriate sequences of computer-readable instructionscontained in main memory 306. Such instructions may be read into mainmemory 306 from another computer-readable medium, such as storage device310, and execution of the sequences of instructions contained in themain memory 306 causes the processor 304 to perform the associatedactions. In alternative embodiments, hard-wired circuitry orfirmware-controlled processing units may be used in place of or incombination with processor 304 and its associated computer softwareinstructions to implement the invention. The computer-readableinstructions may be rendered in any computer language.

In general, all of the above process descriptions are meant to encompassany series of logical steps performed in a sequence to accomplish agiven purpose, which is the hallmark of any computer-executableapplication. Unless specifically stated otherwise, it should beappreciated that throughout the description of the present invention,use of terms such as “processing”, “computing”, “calculating”,“determining”, “displaying”, “receiving”, “transmitting” or the like,refer to the action and processes of an appropriately programmedcomputer system, such as computer system 300 or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within its registers and memories intoother data similarly represented as physical quantities within itsmemories or registers or other such information storage, transmission ordisplay devices.

Computer system 300 also includes a communication interface 318 coupledto the bus 302. Communication interface 318 may provide a two-way datacommunication channel with a computer network, which providesconnectivity to and among the various computer systems discussed above.For example, communication interface 318 may be a local area network(LAN) card to provide a data communication connection to a compatibleLAN, which itself is communicatively coupled to the Internet through oneor more Internet service provider networks. The precise details of suchcommunication paths are not critical to the present invention. What isimportant is that computer system 300 can send and receive messages anddata through the communication interface 318 and in that way communicatewith hosts accessible via the Internet.

Thus, methods and systems for photocuring liquid resin with reduced heatgeneration has been described. It is to be understood that theabove-description is intended to be illustrative, and not restrictive.Many other embodiments will be apparent to those of skill in the artupon reviewing the above description. The scope of the invention should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

What is claimed is:
 1. A vat polymerization printer, comprising: a tank configured for containing a photo-curable liquid resin; a light source configured to emit a light beam; a mask having pixels configurable to be individually transparent or opaque to portions of the light beam, wherein a diameter of a cross section of the light beam is greater than a cross-sectional dimension of each of the respective pixels; a beam scanner configured to scan the light beam across the mask; and a controller comprising a memory and a processor, the memory storing instructions that, when executed, cause the processor to control the vat polymerization printer to print a cross section of a three-dimensional object by: controlling, during an exposure time duration, a first subset of the pixels to be transparent at locations corresponding to the cross section of the three-dimensional object, and a second subset of the pixels to be opaque at locations not corresponding to the cross section of the three-dimensional object; and controlling, during the exposure time duration, the beam scanner to scan the light beam across the mask such that the light beam is always incident on at least one of the pixels of the mask that are controlled to be transparent.
 2. The vat polymerization printer of claim 1, wherein the diameter of the cross section of the light beam is at least ten times the cross-sectional dimension of each of the respective pixels.
 3. The vat polymerization printer of claim 1, wherein the diameter of the cross section of the light beam is at least a hundred times the cross-sectional dimension of each of the respective pixels.
 4. The vat polymerization printer of claim 1, wherein the light source comprises: a laser source configured to emit a laser beam; and a beam expander configured to generate the light beam from the laser beam, wherein the diameter of the cross section of the light beam is greater than a diameter of a cross section of the laser beam.
 5. The vat polymerization printer of claim 1, wherein the instructions further cause the processor to determine a scan path for the light beam based on respective locations of the pixels that are controlled to be transparent during the exposure time duration.
 6. The vat polymerization printer of claim 1, wherein during the exposure time duration, the instructions further cause the processor to turn off the light source while the beam scanner repositions the light beam between a first region of the mask that includes at least some pixels that are controlled to be transparent to a third region of the mask that includes at least some pixels that are controlled to be transparent, the third region of the mask being separate from the first region of the mask by a second region of the mask that includes only pixels that are controlled to be opaque.
 7. The vat polymerization printer of claim 1, wherein the instructions further cause the processor to control a blocking element to block the light beam while the beam scanner repositions the light beam from a first region of the mask that includes at least some pixels that are controlled to be transparent to a third region of the mask that includes at least some pixels that are controlled to be transparent, the third region of the mask being separate from the first region of the mask by a second region of the mask that includes only pixels that are controlled to be opaque.
 8. The vat polymerization printer of claim 1, wherein the pixels comprise electrically modulated liquid crystal pixel elements.
 9. The vat polymerization printer of claim 1, further comprising a transparent backing member disposed between the mask and a flexible membrane.
 10. The vat polymerization printer of claim 1, further comprising: an extraction plate disposed within the tank to which the three-dimensional object, formed from cured portions of the photo-curing liquid resin, is affixed; and a height adjustor configured to control a vertical position of the extraction plate above the mask.
 11. A vat polymerization printer, comprising: a tank configured for containing a photo-curable liquid resin; a light source configured to emit a light beam; a mask having pixels configurable to be individually transparent or opaque to portions of the light beam, wherein a diameter of a cross section of the light beam is greater than a cross-sectional dimension of each of the respective pixels; a beam scanner configured to scan the light beam across the mask; and a controller comprising a memory and a processor, the memory storing instructions that, when executed, cause the processor to control the vat polymerization printer to print a cross section of a three-dimensional object by: controlling, during an exposure time duration, a first subset of the pixels to be transparent at locations corresponding to the cross section of the three-dimensional object, and a second subset of the pixels to be opaque at locations not corresponding to the cross section of the three-dimensional object; and controlling, during the exposure time duration, the beam scanner to scan the light beam across at least one region of the mask having pixels that are controlled to be transparent, wherein at most ten percent of the pixels that are controlled to be opaque are scanned by the light beam during the printing of the cross section of the three-dimensional object.
 12. The vat polymerization printer of claim 11, wherein the instructions further cause the processor to control the beam scanner to repeatedly scan the light beam across a first region of the mask that includes at least some pixels that are controlled to be transparent, followed by controlling the beam scanner to scan the light beam along a beam path within a second region that separates the first region from a third region, the second region including only pixels that are controlled to be opaque, and the third region including at least some pixels that are controlled to be transparent, and the beam path within the second region being a shortest path that connects a beam path in the first region and a beam path in the third region, and followed by controlling the beam scanner to repeatedly scan the light beam across the third region of the mask.
 13. The vat polymerization printer of claim 12, wherein repeatedly scanning the light beam across the first region of the mask comprises at least one of a raster scan or a back and forth scan of the first region of the mask, and wherein repeatedly scanning the light beam across the third region of the mask comprises at least one of a raster scan or a back and forth scan of the third region of the mask.
 14. A method for printing a cross section of a three-dimensional object in a photocuring region of a vat polymerization printer that includes (i) a tank configured for containing a photo-curable liquid resin, (ii) a flexible membrane defining a bottom boundary of the photocuring region, (iii) a light source configured to emit a light beam, (iv) a beam scanner configured to scan the light beam, and (v) a mask disposed between the beam scanner and the flexible membrane and having pixels configurable to be individually transparent or opaque to portions of the light beam, wherein a diameter of a cross section of the light beam is greater than a cross-sectional dimension of each of the respective pixels, the method comprising: controlling, during an exposure time duration, a first subset of the pixels to be transparent at locations corresponding to the cross section of the three-dimensional object, and a second subset of the pixels to be opaque at locations not corresponding to the cross section of the three-dimensional object; and scanning, during the exposure time duration, the light beam across at least one region of the mask having at least some pixels that are controlled to be transparent and into the photocuring region, wherein at most ten percent of the pixels that are controlled to be opaque are scanned by the light beam during the printing of the cross section of the three-dimensional object.
 15. The method of claim 14, wherein, during the exposure time duration, and as a result of the control of the first and second subset of the pixels, a first region of the mask includes at least some pixels that are controlled to be transparent, a second region of the mask includes only pixels that are controlled to be opaque, and a third region of the mask includes at least some pixels that are controlled to be transparent, and wherein the scanning of the light beam comprises repeatedly scanning the light beam across the first region of the mask and into the photocuring region through pixels in the first region that are controlled to be transparent, followed by scanning the light beam along a shortest path, within the second region, that connects a beam path in the first region and a beam path in the third region, and followed by repeatedly scanning the light beam across the third region of the mask and into the photocuring region through pixels in the third region that are controlled to be transparent.
 16. The method of claim 15, wherein repeatedly scanning the light beam across the first region of the mask comprises at least one of a raster scan or a back and forth scan of the first region of the mask, and wherein repeatedly scanning the light beam across the third region of the mask comprises at least one of a raster scan or a back and forth scan of the third region of the mask.
 17. The method of claim 14, wherein, during the exposure time duration, and as a result of the control of first and second subset of the pixels, a first region of the mask includes at least some pixels that are controlled to be transparent, a second region of the mask includes only pixels that are controlled to be opaque, and a third region of the mask includes at least some pixels that are controlled to be transparent, and wherein the scanning of the light beam comprises repeatedly scanning the light beam across the first region of the mask and into the photocuring region through pixels of the first region that are controlled to be transparent, repositioning the light beam from the first region of the mask to the third region of the mask without scanning the second region of the mask, and repeatedly scanning the light beam across the third region of the mask and into the photocuring region through pixels of the third region that are controlled to be transparent.
 18. The method of claim 17, wherein repeatedly scanning the light beam across the first region of the mask comprises at least one of a raster scan or a back and forth scan of the first region of the mask, and wherein repeatedly scanning the light beam across the third region of the mask comprises at least one of a raster scan or a back and forth scan of the third region of the mask.
 19. The method of claim 14, wherein, during the exposure time duration, a total number of pixels in the first subset of the pixels is less than a total number of pixels in the second subset of the pixels.
 20. A method for printing a cross section of a three-dimensional object in a photocuring region of a vat polymerization printer that includes (i) a tank configured for containing a photo-curable liquid resin, (ii) a flexible membrane defining a bottom boundary of the photocuring region, (iii) a light source configured to emit a light beam, (iv) a beam scanner configured to scan the light beam, and (v) a mask disposed between the beam scanner and the flexible membrane and having pixels configurable to be individually transparent or opaque to portions of the light beam, wherein a diameter of a cross section of the light beam is greater than a cross-sectional dimension of each of the respective pixels, the method comprising: controlling, during an exposure time duration, a first subset of the pixels to be transparent at locations corresponding to the cross section of the three-dimensional object, and a second subset of the pixels to be opaque at locations not corresponding to the cross section of the three-dimensional object; and scanning, during the exposure time duration, the light beam across at least one region of the mask having at least some pixels that are controlled to be transparent and into the photocuring region, wherein the scanning compensates for a non-uniformity in a light transmission across respective pixels in the at least one region of the mask by at least one of: (i) varying a light intensity of the light beam while the light beam is scanned over the at least one region, (ii) varying a scan speed of the light beam while the light beam is scanned over the at least one region, or (iii) varying a number of times the light beam is repeatedly scanned over the at least one region. 